Deploy voting app on Kubernetes

Learn how to deploy a containerized voting application on Kubernetes. In this guide, we’ll walk through deploying each component as a container, configuring intra-cluster connectivity, and exposing the frontend services externally.

Objectives

• Deploy each service as containers on a Kubernetes cluster
• Enable reliable connectivity so services can communicate
• Expose the Voting and Result apps externally via web browser

High-Level Plan

1. Deploy each application as a standalone Pod (we’ll convert them to Deployments later).
2. Create Services for internal connectivity:
   • redis (ClusterIP)
   • db (ClusterIP)
3. Expose the frontends using NodePort Services:
   • voting-app
   • result-app
4. Skip a Service for the worker (it’s only a background job).

Connectivity Requirements

• voting-app writes votes to Redis.
• worker reads votes from Redis and writes aggregates to PostgreSQL.
• result-app reads results from PostgreSQL to display.
• voting-app and result-app are user-facing.
• worker runs in the background and doesn’t receive external traffic.

Each component listens on its own port:

• voting-app: 80
• result-app: 80
• redis: 6379
• postgres: 5432
• worker: no external port

Why Use a Service?

Pod IPs are ephemeral. Kubernetes Services provide a stable DNS name and virtual IP. For example, the Python app connects to Redis at host redis:

# app.py
from flask import Flask, g
from redis import Redis

app = Flask(__name__)

def get_redis():
    if not hasattr(g, 'redis'):
        g.redis = Redis(host="redis", db=0, socket_timeout=5)
    return g.redis

And in C# the services connect using the Service DNS names:

// Program.cs
var pgsql = OpenDbConnection("Server=db;Username=postgres;Password=postgres;");
var redisConn = OpenRedisConnection("redis");
var redis = redisConn.GetDatabase();

Database Credentials

• Username: postgres
• Password: postgres

Service Types

• ClusterIP: Internal-only (redis, db)
• NodePort: External access (voting-app, result-app) – ports > 30000

Summary of Resources

Docker Images

We’ll use the following container images:

• kodekloud/example-voting-app_vote:v1
• kodekloud/example-voting-app_worker:v1
• kodekloud/example-voting-app_result:v1
• redis:latest
• postgres:latest

In the next section, we’ll create the Pods and Services and test the end-to-end workflow of the voting application.

Links and References

• Kubernetes Services
• Kubernetes Pods
• Flask Redis Client
• Npgsql .NET Driver